U.S. Pat. No. 3,783,977 discloses a door drive device for opening and closing car door leaves of an elevator car door, wherein the door drive device comprises a car door locking mechanism. The door drive device is activated by means of a crank drive and comprises two coupling devices for transmitting the opening and closing movement from the car door leaves to corresponding shaft door leaves. The coupling devices each comprise two entraining rails which are guided on the car door leaf on pivotable connector levers and which can interact with, in each case, two opposite elements on the corresponding shaft door leaves when the elevator car is located at the level of a floor. The horizontal distance between two associated entraining rails can be changed by pivoting the connector levers, wherein the pivoting movements of the connector levers are generated by the crank drive in such a way that, when doors are closed, a minimum horizontal distance is present and therefore no interaction takes place between the entraining rails of the car door leaves and the opposite elements of the shaft door leaves, and therefore an increased horizontal distance is produced between the entraining rails when the doors are not closed. When the elevator car is located at the level of a floor, the increased horizontal distance between the entraining rails brings about a play-free coupling between the entraining rails and the opposite elements of corresponding car door leaves or shaft door leaves, wherein the horizontal distance between the entraining rails, and therefore the pivoting position of the connector levers, is limited by the opposite elements. If no such limitation takes place because the elevator car is not located at the level of a floor, there is a resulting increase in the specified horizontal distance and therefore in the pivoting travel of the connector levers. One of the pivoting levers has an extension which interacts with a stop (secured to the door frame) in such a way that the opening of the assigned car door leaf is blocked, when the specified horizontal distance between the entraining rails and therefore the pivoting position of the connector levers is not limited by the opposite elements on the corresponding shaft door leaf.
The door drive device which is known from U.S. Pat. No. 3,783,977, and which has a simple and cost-effective car door locking mechanism, has the disadvantage that the car door locking mechanism acts only when a triggered coupling process has not brought about coupling between the entraining rails and the opposite elements, because the elevator car is located above or below the level of a floor. The regulation which is contained in elevator standards, and which requires a car door locking mechanism to prevent any opening process outside the level of a floor in certain embodiments of the elevator system, is not satisfied by this car door locking mechanism.
Patent EP 0 332 841 B1 discloses a door drive device with a coupling mechanism for coupling a car door leaf to an assigned shaft door leaf. The coupling mechanism comprises two entraining runners which are oriented parallel to the direction of travel of the elevator car, and the distance between which can be adjusted by means of a parallelogram guide with two adjustment elements which can each pivot about a pivoting axis. When the elevator car is located at the level of a floor within permissible misalignments, the two entraining runners are located between two opposite elements arranged one next to the other on the shaft door leaf, and said entraining runners can be made to approach the latter laterally (can be spread) in order, on the one hand, to unlock the shaft door leaf and, on the other hand, to transmit the opening movement and closing movement of the car door without play and synchronously to the shaft door leaf. The distance adjustment between the two entraining runners is carried out here by means of a door drive unit which is attached to the car door frame, via a linearly acting drive means (for example by means of a belt drive) which also brings about the closing movements and opening movements of the car door leaf. In the process, the drive means engages, via a pivoting lever connected to the adjustment elements of the parallelogram guide, on the car door leaf in such a way that, before the start of a door leaf opening movement, the adjustment elements are pivoted, by the opening movement of the linearly acting drive means, into a position in which the entraining runners are made to approach the opposite elements, and as a result unlock the shaft door leaf and form the specified coupling between the car door leaf and the corresponding shaft door leaf.
At the end of a door leaf closing movement, the adjustment elements are pivoted, by the closing movement of the linearly acting drive means, back into a position in which the entraining runners are spaced apart from the opposite elements, so that the locking mechanism of the shaft door leaf returns to its locking position.
EP 0 332 841 B1 also discloses a device for unlocking the bolt of a car door locking mechanism which is intended to ensure that the car door is unlocked automatically only if the car door is located opposite a shaft door of the elevator.
For this purpose, one of the entraining runners has a sensing runner in the region of its outer runner face, i.e. the runner face which interacts with the corresponding opposite element on the shaft door leaf (coupling roller). Said sensing runner extends parallel to the entraining runner, and is connected thereto by means of connector springs in such a way that in the unloaded state said sensing runner is spaced apart from the entraining runner by several millimeters. The contact force which is applied to the sensing runner during a coupling process (entraining spreading) by the opposite element causes said sensing runner to move counter to the spring force of the connector springs in the direction of the entraining runner. The sensing runner has a cam which transmits its movement, brought about by the opposite element, with respect to the entraining runner and therefore with respect to the car door leaf to a car door bolt which is mounted on this car door leaf, and said cam unlocks the car door leaf. If a door opening command is issued and resulting spreading of the entraining runners of the coupling mechanism occurs when the door of the elevator car is not located opposite a shaft door, the entraining runners, like the sensing runner, do not enter into contact with one of the opposite elements on the shaft door leaves. The sensing runner is therefore not moved against the entraining runner, and the car door bolt remains in its locking position. A sensor which monitors the position of the car door bolt additionally prevents the door drive motor from switching on.
The illustrated coupling mechanism with a car door unlocking mechanism requires on one of the entraining runners a sensing runner which can move relative to the latter and is guided in parallel, which is associated with a high degree of expenditure in terms of material and fabrication. The relatively small sensing travel of the sensing runner requires a lever system with a large transmission ratio, in order to generate sufficient unlocking travel at the car door bolt. This requires the coupling device and the car door unlocking device to be fabricated with high precision. Furthermore, jolt-like accelerations of the car door bolt result from the large transmission ratio when the sensing runner strikes against the opposite element, and this can result in undesired noises.
A further device for coupling a car door leaf of an elevator car to a corresponding shaft door leaf, which device interacts with a car door locking mechanism, is known from EP 1 541 517 A1. The method of functioning of said device corresponds largely to that of the device according to EP 0 332 841 B1 which is described above. In contrast to the device according to EP 0 332 841 B1, a sensing runner is not arranged on an entraining runner in the device according to EP 1 541 517 A1, but instead the function of the sensing runner is integrated into one of the entraining runners. This is implemented by virtue of the fact that this entraining runner is connected via joint elements to the pivotable adjustment elements, which through their pivoting movement change the distance between the entraining runners.
The device known from EP 1 541 517 A1 has essentially the same disadvantages as those mentioned above in conjunction with the device according to EP 1 541 517 A1.